1963] Eisner , Elurst and Meinwald — Defense Mechanisms 
IOI 
The reservoir leads to the outside by way of a narrow duct, the 
terminal portion of which is occluded by a valvular infolding of the 
cuticular duct wall. A single muscle (Plate 12, fig. 4, A) inserts on 
this infolding, and extends to its origin on the body wall. It obviously 
serves to open the valve, clearing the duct lumen for the discharge. 
In the absence of compressor muscles around the reservoir, there 
remains the question of how secretion is expelled. Perhaps compression 
is effected indirectly by the contraction of some of the somatic muscles 
that tightly surround the reservoirs. But it is also conceivable that 
the discharge is triggered by a rise in fluid pressure within the hemo- 
coel, caused perhaps by a local telescoping of segments. These two 
possbilities need not be mutually exclusive. 
II. Identification of the Phenolic Constitutents of the Secretions, 
a. ra-Cresol (m-methylphenol) in Chlaenius. 
A total of ten glands were excised intact from beetles that had 
been freshly killed by freezing, and the secretion (a milky white 
emulsion) was aspiratd into fine glass capillaries as it emerged from 
the ejaculatory ducts, following compression of the reservoirs with 
forceps. The entire glandular apparatus was previously blotted dry 
with filter paper, thus minimizing the amount of extraneous fluid 
taken with this secretion. The capillaries were powdered in a small 
mortar and extracted with carbon disulfide. The solution was then 
dried over anhydrous magnesium sulfate, and concentrated by evapo- 
ration of the solvent in a stream of nitrogen. The infrared spectrum 
of the residual solution (Model 137 Perkin Elmer Infracord Spectro- 
photometer; 0.5 mm. liquid cells with KBr windows) was similar 
in all major respects to that of an authentic sample of m-cresol (Text 
fig. 2). The discrepancy in the region of C-H stretching ( ca . 3.5 /x) 
and in the carbonyl region (ca. 5.8 /a) suggests that m-cresol is not 
the only component of the natural product. 
The presence of m-cresol was confirmed by vapor phase chroma- 
tography (Aerograph Model 600 “Hy-Fi”, using 3% neopentyl glycol 
EXPLANATION OF PLATE 10 
Figs. 1-4. Four consecutive discharges of Chlaenius , elicited by pinching 
with forceps individual pro- and metathoracic legs as shown. The spray 
pattern is registered on filter paper impregnated with a chemical indicator 
(see text, part I). 
Fig. 5. An individual Chlaenius, after having been caused to discharge, 
was transferred from place to place on a sheet of indicator paper. As long 
as residual secretion remained on its body and feet, a conspicuous discolored 
zone developed around it at each locus (the dark spots within each zone are 
footprints). Transfer was at two-minute intervals; the times given are from 
the moment of discharge. 
